Apparatus and method for automatically compensating for lateral runout

ABSTRACT

An on-car disc brake lathe system for resurfacing a brake disc of a vehicle brake assembly includes a lathe body with a driving motor, a cutting head operably attached to the lathe body, and a drive shaft. The system also includes an alignment system having an electronic controller, input and output adaptors configured to rotate with the drive shaft, one or more adjustment discs, and an adjustment mechanism. The adjustment disc is positioned between the input adaptor and the output adaptor, and an axial alignment of the input adaptor relative to the output adaptor may be varied based on a rotational orientation of the adjustment disc. The adjustment mechanism is configured to change the rotational orientation of the adjustment disc in response to commands from the electronic controller.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. Nos. 08/706,512 and 08/706,514, filed Sep. 4, 1996, andincorporated by reference.

TECHNICAL FIELD

[0002] The invention relates to on-car brake lathes.

BACKGROUND

[0003] A brake system is one of the primary safety features in everyroad vehicle. The ability to quickly decelerate and bring a vehicle to acontrolled stop is critical to the safety of the vehicle occupants andthose in the immediate vicinity. For this reason, a vehicle brakingsystem is designed and manufactured to exacting specifications and issubject to rigorous inspection.

[0004] Disc brake assemblies, which are typically mounted on the frontwheels of most passenger vehicles, are primary components of a brakesystem. Generally, a disc brake assembly includes a caliper thatcooperates with a brake hydraulic system, a pair of brake pads, a hub,and a rotor. The caliper supports and positions the pair of brake padson opposing sides of the brake rotor. In a hubless brake rotor (i.e.when the rotor and hub are separate components), the rotor is secured tothe vehicle hub with a series of bolts and a rotor hat. The rotorrotates with the hub about a vehicle spindle axis. When a vehicle driverdepresses a brake pedal to activate the hydraulic system, the brake padsare forced together and toward the rotor to grip friction surfaces ofthe rotor.

[0005] Disc brake assemblies must be maintained to the manufacturer'sspecifications throughout the life of the vehicle to assure optimumperformance and maximum safety. However, several problems have plaguedthe automotive industry since the inception of disc brakes.

[0006] A significant problem in brake systems is usually referred to as“lateral runout.” Generally, lateral runout is the side-to-side movementof the friction surfaces of the rotor as the rotor rotates with thevehicle hub about a spindle axis. Referring to FIG. 1, for example, arotor having friction surfaces on its lateral sides is mounted on avehicle hub for rotation about the horizontal spindle axis X. In anoptimum rotor configuration, the rotor is mounted to rotate in a plane Ythat is precisely perpendicular to the spindle axis X. Generally, goodbraking performance is dependant upon the rotor friction surfaces beingperpendicular to the spindle's axis of rotation X and being parallel toone another. In the optimum configuration, the opposing brake padscontact the friction surfaces of the rotor at perfect 90 degree anglesand exert equal pressure on the rotor as it rotates. More typically,however, the disc brake assembly produces at least a degree of lateralrunout that deviates from the ideal configuration. For example, a rotoroften will rotate in a canted plane Y′ and about an axis X′ that is afew thousandths of an inch out of axial alignment with the spindle(shown in exaggerated fashion in FIG. 1). In this rotor configuration,the brake pads, which are perpendicular to the spindle axis X, do notcontact the friction surfaces of the rotor along a constant pressureplane.

[0007] The lateral runout of a rotor is the lateral distance that therotor deviates from the ideal plane of rotation Y during a rotationcycle. A certain amount of lateral runout is inherently present in thehub and rotor assembly. This lateral runout often results from defectsin individual components. For example, rotor friction surface runoutresults when the rotor friction surfaces are not perpendicular to therotor's own axis of rotation, rotor hat runout results when the hatconnection includes deviations that produce an off center mount, andstacked runout results when the runouts of the components are added or“stacked” with each other. An excessive amount of lateral runout in acomponent or in the assembly (i.e., stacked runout) will generallyresult in brake noise, pedal pulsation, and a significant reduction inoverall brake system efficiency. Moreover, brake pad wear is uneven andaccelerated with the presence of lateral runout. Typically,manufacturers specify a maximum lateral runout for the frictionsurfaces, rotor hat, and hub that is acceptable for safe and reliableoperation.

[0008] After extended use, a brake rotor must be resurfaced to bring thebrake assembly within manufacturers' specifications. This resurfacing istypically accomplished through a grinding or cutting operation. Severalprior art brake lathes have been used to resurface brake rotors. Theseprior art lathes can be categorized into three general classes: (1)bench-mounted lathes; (2) on-car caliper-mounted lathes; and (3) on-carhub-mounted lathes.

[0009] In general, bench-mounted lathes are inefficient and do not haverotor matching capabilities. To resurface a rotor on a bench-mountedlathe, the operator is first required to completely remove the rotorfrom the hub assembly. The operator then mounts the rotor on the benchlathe using a series of cones or adaptors. After the cutting operation,the operator remounts the rotor on the vehicle spindle. Even if therotor is mounted on the lathe in a perfectly centered and runout-freemanner, the bench lathe resurfacing operation does not account forrunout between the rotor and hub. In addition, bench lathes aresusceptible to bent shafts which introduce runout into a machined rotor.This runout is then carried back to the brake assembly where it maycombine with hub runout to produced a stacked runout effect.

[0010] Similarly, caliper-mounted lathes have had limited success incompensating for lateral runout, and require time consuming manualoperations. During a rotor resurfacing procedure, the brake caliper mustbe removed to expose the rotor and hub.

[0011] Once this is done, the caliper mounting bracket is used to mountthe on-car caliper-mounted lathe. Caliper-mounted lathes lack a “rigidloop” connection between the driving motor and cutting tools, and areunable to assure a perpendicular relationship between the cutting toolsand the rotor. Nor does a typical caliper-mounted lathe have a reliablemeans for measuring and correcting lateral runout. Typically, suchlathes use a dial indicator to determine the total amount of lateralrunout in the disc assembly. This measurement technique is problematicin terms of time, accuracy, and ease of use.

[0012] On-car hub-mounted lathes, generally are the most accurate andefficient means for resurfacing the rotor. Such a lathe is disclosed inU.S. Pat. No. 4,226,146, which is incorporated by reference.

[0013] Referring now to FIG. 2, an on-car disc brake lathe 10 may bemounted to the hub of a vehicle 14. The lathe 10 includes a body 16, adriving motor 18, an adaptor 20, and a cutting assembly 22 includingcutting tools 23. The lathe may be used with a stand or an anti-rotationpost (not shown), either of which can counter the rotation of the latheduring a resurfacing operation. After the brake caliper is removed, theadaptor 20 is secured to the hub of the vehicle 14 using the wheel lugnuts. The lathe body 16 is then mounted to the adaptor 20, theorientation of which may be adjusted using adjustment screws 24.

[0014] The operator then determines the total amount of lateral runoutand makes an appropriate adjustment. Specifically, the operator mounts adial indicator 26 to the cutting head 22 using a knob 28. The dialindicator 26 is positioned to contact the vehicle 14 at one of itsdistal ends as shown in FIG. 2. Once the dial indicator 26 is properlypositioned, the operator takes the following steps to measure andcompensate for lateral runout:

[0015] (1) The operator mates the lathe to the rotor using the adaptor.

[0016] (2) The operator activates the lathe motor 18, which rotates theadaptor 20, the brake assembly hub, and the rotor. The total lateralrunout of the assembly is reflected by corresponding lateral movement inthe lathe body.

[0017] (3) The lateral movement of the lathe body is then quantifiedusing the dial indicator 26. Specifically, the operator observes thedial indicator to determine the high and low deflection points and thecorresponding location of these points on the lathe.

[0018] (4) Upon identifying the highest deflection of the dialindicator, the operator stops the rotation at the point of theidentified highest deflection.

[0019] (5) The operator then adjusts the lathe to compensate for runoutof the assembly. This is accomplished by careful turning of theadjustment screws 24. There are four adjustment screws. The screw orscrews to be turned depend on the location of the high deflection point.Turning the screws adjusts the orientation of the lathe body withrespect to the adaptor 20 (and therefore with respect to the rotor andhub) to mechanically compensate for the runout of the assembly. Theoperator adjusts the screws until the highest deflection point isreduced by half as determined by reference to the dial indicator 26.

[0020] (6) The operator activates the lathe motor 18 and observes thedial indicator 26 to again identify the highest deflection of the dial.If the maximum lateral movement of the lathe body, as measured by theneedle deflection, is acceptable (i.e. typically less than {fraction(3/1000)} of an inch) then mechanical compensation is complete and thelathe resurfacing operation can commence. Otherwise, further measurementand adjustment is made by repeating steps (1) to (6). The resurfacingoperation is then performed by adjusting the tool holder 22 and cuttingtools 23 to set the proper cutting depth.

[0021] Although the hub mounted on-car brake lathe was a considerableadvance over prior brake lathes, its structure and the correspondingprocedure for compensating for lateral runout of the disc brake assemblyhas practical limitations. First, the procedure requires a significantamount of time to determine and adjust for lateral runout of the brakeassembly. Although the specific amount of time necessary will vary basedupon operator experience, the time for even the most experiencedoperator is significant and can substantially increase the costassociated with rotor resurfacing. Second, the procedure requiresextensive education and operator training to assure that propermechanical compensation for lateral runout is accomplished. Moreover,the accuracy and success of measurement and adjustment of lateral runoutwill vary from operator to operator.

SUMMARY

[0022] In one general aspect, an on-car disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly includes a lathebody with a driving motor, a cutting head operably attached to the lathebody, and a drive shaft. The system further includes an alignment systemincluding an electronic controller, an input adaptor configured torotate with the drive shaft, an output adaptor configured to rotate withthe drive shaft, and at least one adjustment disc positioned between theinput adaptor and the output adaptor. Axial alignment of the inputadaptor relative to the output adaptor may be varied based on arotational orientation of the adjustment disc. An adjustment mechanismchanges the rotational orientation of the adjustment disc in response tocommands from the electronic controller.

[0023] Embodiments may include one or more of the following features.For example, the adjustment mechanism may include a stop disc operablein a first state to follow the rotation of the drive shaft and operablein a second state to rotate relative to the rotation of the drive shaftto change the rotational orientation of the adjustment disc. Theadjustment mechanism may include a stop mechanism associated with thestop disc and operable to move between a first position in which thestop disc operates in the first state and a second position in which thestop disc is caused to operate in the second state. The stop disc mayinclude a pair of stop discs, with the first stop disc operating in thefirst state when the stop mechanism is in the first position, in thesecond state when the stop mechanism is in the second position at afirst time, and in the first state when the stop mechanism is in thesecond position at a second time different from the first time. Thesecond stop disc operates in the first state when the stop mechanism isin the first position and when the stop mechanism is in the secondposition at the first time, and operates in the second state when thestop mechanism is in the second position at the second time.

[0024] The system may include a second adjustment disc positionedbetween the input adaptor and the output adaptor. The axial alignment ofthe input adaptor relative to the output adaptor may be varied based onthe rotational orientation of the adjustment discs relative to eachother. A stop disc or a pair of stop discs may be associated with eachadjustment disc. A single stop mechanism may be associated with all ofthe stop discs. Gear trains may be associated with the stop discs, andmay be configured to follow the movement of the respective stop discs,and to cause movement of the adjustment discs.

[0025] The adjustment discs may be slant discs that each include aslanted surface. The adjustment discs may be arranged so that theslanted surfaces are opposed to each other in an abutting relationship.

[0026] The stop discs may be starwheels having protruding teeth. Thestop mechanism may be operable to move between a first position in whichthe stop disc operates in the first state and a second position in whichthe stop disc is caused to operate in the second state. For example, thestop mechanism may include an electromagnetic element and a toothedcatch member operable to engage at least one tooth of the starwheel. Thecontroller may be configured to time actuation of the electromagneticelement such that the toothed catch moves into its first stop positionto contact a specified tooth of the starwheel.

[0027] The system also may include a component for measuring lateralrunout of a brake disc and providing the measurement to the electroniccontroller. The electronic controller may issue commands to theadjustment mechanism based on the measurement.

[0028] The systems and techniques provide automatic compensation for thelateral runout of a lathe apparatus with respect to a vehicle hub. Tothis end, the brake lathe system includes a runout measurement andcontrol system that determines the runout of a disc brake assembly anddirects a corrective signal to an automated control system to compensatefor lateral runout. The techniques may also be used in other practicalapplications to align two concentrically attached rotating shafts.

[0029] To provide automatic compensation for lateral runout, a brakelathe includes an automatic alignment coupling that operates in responseto a corrective signal to adjust the alignment of the lathe with respectto the vehicle to mechanically compensate for lateral runout. Theautomatic alignment mechanism may include one or more stop discs thatrotate with the drive shaft of the lathe and that can be selectivelystopped from rotating with the shaft by a stop mechanism. In response tosuch stopping, one or more adjustment discs are caused to rotate toadjust the relative position of the axis of the lathe with respect tothe axis of the disc brake assembly. In this manner, the systemcompensates for and corrects lateral runout that exists between twoconcentrically attached rotating shafts. Other techniques may also beused to compensate for the lateral runout.

[0030] Other features and advantages will be apparent from the followingdescription, including the drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0031]FIG. 1 is a graphical representation of a lateral runoutphenomenon.

[0032]FIG. 2 is a plan view showing an on-car disc brake lathe anddepicting a prior art procedure for measuring, and compensating forlateral runout of a disc brake assembly.

[0033]FIG. 3 is a perspective view showing an on-car disc brake lathemounted on the hub of a vehicle in preparation for a disc resurfacingoperation.

[0034]FIG. 4 is a partially sectional schematic view of a disc brakelathe with an automatic alignment apparatus.

[0035]FIGS. 5A and 5B are cross-sectional and front views, respectively,of the automatic alignment apparatus of FIG. 4.

[0036]FIG. 6 is a cross-sectional view of the adjustment disc assembliesof the automatic alignment apparatus of FIG. 4.

[0037]FIGS. 7A and 7B are front cross-sectional views of one of theadjustment disc assemblies of the automatic alignment apparatus of FIG.4.

[0038]FIGS. 8 and 9 are cross-sectional views of the adjustment discassemblies of the automatic alignment apparatus of FIG. 4.

[0039]FIGS. 10A and 10B are cross-sectional and side views,respectively, of an automatic alignment apparatus.

[0040] FIGS. 10C and 10C-1 are front and cross-sectional views,respectively, of an adjustment disc of the automatic alignment apparatusof FIGS. 10A and 10B.

[0041] FIGS. 10D and 10D-1 are front and cross-sectional views,respectively, of a slant disc of the automatic alignment apparatus ofFIGS. 10A and 10B.

[0042]FIGS. 11A and 11B are schematic representations of thecompensation vector and compensation alignment angle of the automaticalignment apparatus of FIGS. 10A and 10B.

[0043]FIG. 12 is a cross-sectional view of an automatic alignmentapparatus.

[0044]FIGS. 13A and 13B are front views of input and output adaptorassemblies and a front view of the drive arm assembly, respectively, ofthe automatic alignment apparatus of FIG. 12.

[0045]FIG. 14 is a front view of a starwheel stop mechanism of theautomatic alignment apparatus of FIG. 12.

[0046]FIG. 15A is a timing diagram of the hall transducer timing pulseduring the starwheel stop operation of the automatic alignment apparatusof FIG. 12.

[0047]FIG. 15B is a timing diagram of the forward starwheel positionduring the starwheel stop operation of the automatic alignment apparatusof FIG. 12.

[0048]FIG. 15C is a timing diagram of the forward starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

[0049]FIG. 15D is a timing diagram of the forward starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

[0050]FIG. 15E is a timing diagram of the reverse starwheel positionduring the starwheel stop operation of the automatic alignment apparatusof FIG. 12.

[0051]FIG. 15F is a timing diagram of the reverse starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

[0052]FIG. 15G is a timing diagram of the reverse starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

[0053]FIG. 16 is a flow diagram of an automatic alignment operationusing the automatic alignment apparatus of FIG. 12.

[0054]FIG. 17 is a schematic view of the rotational runout phenomenonoccurring during a cutting operation of the on-car disc brake lathemounted on the hub of a vehicle.

[0055]FIG. 18 is a schematic view of the linear runout phenomenonoccurring during a cutting operation of the on-car disc brake lathemounted on the hub of a vehicle.

[0056]FIGS. 19A and 19B are front and cross-sectional views,respectively, of a rotary piezo-electric accelerometer.

[0057]FIG. 20 is a front view of a rotary tuned coil oscillatoraccelerometer.

[0058]FIG. 21 is a front view of a rotary magnetic hall effecttransducer.

[0059]FIGS. 22 and 22A are front and side views of a rotary infraredgenerator accelerometer.

[0060]FIGS. 23 and 23A are front and side views of a rotaryaccelerometer employing a magnetic spring.

[0061]FIGS. 24 and 24A are side and top views of a rotary accelerometeremploying a magnetic spring and electrical heating.

[0062]FIG. 25 is a circuit diagram of a control system of a runoutmeasurement and control system.

[0063]FIGS. 26 and 28 are section side views of a runout adjustmentmechanism.

[0064]FIGS. 27 and 29 are end views of the mechanism of FIG. 26.

[0065]FIGS. 30 and 31 are timing diagrams associated with the mechanismof FIG. 26.

[0066]FIGS. 32 and 33 are side and end views of a ball-and-socket jointadaptor.

[0067]FIGS. 34 and 35 are side and end views of an adaptor usingservo-controlled extenders.

DETAILED DESCRIPTION

[0068] Referring to FIG. 3, an on-car disc brake lathe 30 is mounted toa hub 31 of a brake assembly of a vehicle 14. The brake lathe 30includes a motor 32, a body 34, a cutting head 36 with cutting tools 38,and an adaptor 40. The vehicle disc brake assembly includes a rotor 42operably attached to the hub 31. Typically, the attachment of the rotor42 to the hub is through a rotor hat (not shown) formed in the rotor 42(i.e., the rotor is a “hubless” rotor). However, an integral rotor andhub may occasionally be used in commercial vehicles. The adaptor 40 ismounted to the hub 31 of the vehicle using the lug nuts 46 normally usedto secure the hub 31 to a wheel.

[0069] FIGS. 4-19 illustrate a on-car disc brake lathe with an automaticalignment and compensation mechanism. Referring to FIG. 4, a lathe 48includes an automatic alignment mechanism 50, a lathe housing or body52, a hub adaptor 54, and a drawbar assembly 56. The hub adaptor 54corresponds to the adaptor 40 of the lathe 30, and is used to connectthe lathe 48 to the hub 31 of a vehicle 14. The drawbar assemblyincludes a drawbar 58 that extends through the body 52 and alignmentmechanism 50.

[0070] The drawbar 58 is operably connected to the adaptor 54 by athreaded connection (as shown) or the like. A calibration knob 60 istightened during the automated alignment sequence of the lathe. Afteralignment is complete, a run knob 62 is tightened for the cuttingoperation. Spring 64 is a belleville washer that provides a loadingforce on bar 58 and the other components of the lathe.

[0071] Referring to FIGS. 5A and 5B, the automatic alignment coupling 50includes an input adaptor 66 operably attached to a rotating drive shaftof the lathe machine (shown in phantom in FIG. 4). A shaft 68 isattached to the input adaptor 66 such that the mounting face of theadaptor 66 is perpendicular to the shaft 68 axis so that shaft 68 runstrue with the axis of the lathe machine.

[0072] Two slant or adjustment disc assemblies 70 and 72 are interposedbetween the input adaptor 66 and an alignment drive disc 74 which isattached to the shaft 68 and caused to rotate with the shaft by a key 76and a set screw 78. A pivot plate 80 is operably attached to an outputadaptor 82 and mounted to the shaft 68 by a spherical bearing 84 topermit the pivot plate 80 to pivot in relation to shaft 68 while beingconstrained from radial movement.

[0073] A pin 86, inserted into pivot plate 80, fits into a slot 88 atthe periphery of the drive disc 74 and rotationally couples the pivotplate 80 to the shaft 68 and the input adaptor 66. As such, when theinput adaptor 66 is mounted on the lathe machine's drive shaft and theoutput adaptor 82 is mounted on the automobile brake disc adaptor 54,the lathe machine output rotation causes the automobile brake discadaptor 54 to rotate, which causes the brake disc to rotate.

[0074] The slant or adjustment disc assemblies 70 and 72, which aremirrors of each other, are placed between the input adaptor 66 and theoutput adaptor 82 as shown. The axial force produced by the axiallymounted drawbar 58 causes the output adaptor 82 to be forced againstslant disc assembly 72 and to assume an angle to the shaft 68 thatdepends upon the relative rotational positions of the slant discs 90 and92, which are controlled using stop discs 94 and 96.

[0075] Control of the relative rotational positions of the slant discs90 and 92 is accomplished while the lathe machine output shaft isdriving the automobile brake disc hub. Specifically, by stopping therotation of stop disc 94 or 96, its associated slant disc is caused torotate in relation to the other slant disc, thus producing a change inangle of the output of the adjustment disc assemblies 70 and 72 and acorresponding change in the angle of the output adaptor 82. This causesa change in the angular alignment of the lathe machine axis and theautomobile brake disc axis.

[0076] The stop discs 94 and 96 are selectively stopped by poweringrespective electromagnetic catches 98 and 100. The catches arecontrolled by a microprocessor system that operates in conjunction witha runout measurement and control mechanism described in more detailbelow. The lathe machine output shaft rotates at a speed that is toofast (for example, 123.14 RPM) to allow stop and release of a stop discand associated slant disc for adjustment. As such, the rotation speed ofthe adjustment components is slowed using a gear train contained in eachof the slant disc assemblies. The gear train extends the time permittedfor adjustments in a given ½ revolution of the shaft 68 (i.e. the timeit takes to stop the relative rotation of the slant discs in {fraction(1/2)} revolution for maximum angular runout adjustment). For example,the time at a shaft rotation rate of 123.14 RPM extends from 0.243seconds for {fraction (1/2)} revolution of the shaft 68 to 3.297 secondsto permit easy and complete adjustment of the slant disc assemblies 70and 72.

[0077] Referring to FIGS. 6 and 7A, the gearing mechanism includes agear 102 containing 88 teeth. Gear 102 is coupled to rotate with shaft68 by a key 104. A gear 106 contains 38 teeth and is mounted on a pivot108 formed on stop disc 94. Thus, when stop disc 94 is stopped by theelectromagnetic catch 98, gear 106 rotates at a much faster rate thanshaft 68. For example, if shaft 68 rotates at 123.14 RPM, gear 106rotates at 285.166 RPM. A gear 110, also mounted on pivot 108, isprovided with 36 teeth and is pinned to rotate with gear 106. Gear 110is coupled to a gear 112 that is provided with, for example, 90 teeth.As such, gear 112 rotates at 114.06 RPM, or 92.6 percent of therotational speed of shaft 68, and rotates backwards in relation to shaft68 and slant disc 92. Because slant disc 90 is pinned to gear 112, italso moves backwards in relation to shaft 68. The gear arrangement andstop discs permit the adjustment of the slant disc assemblies, andtherefore, the alignment of the lathe drive axis and the hub axis,without the need for a separate motor or power source. It is to beunderstood that the identified gear ratios and rotation speeds arepractical examples and are not intended to limit the scope of theinvention. When the stop disc 94 is released, the stop disc 94 and slantdisc 90 again rotate at the rate of the shaft 68.

[0078] A stop pin 114 secured to slant disc 92 stops the relativerotation of the slant discs at {fraction (1/2)} revolution, with stopdisc 94 being parallel with stop disc 96 at one extreme and beingpositioned to provide maximum angular runout at the other extreme. Bystopping the rotation of both stop discs 94 and 96, adjustment disc 90and 92 remain fixed in relation to each other. Stopping the rotation ofstop disc 94 alone until stop pin 114 couples to slant disc 90 causesstop disc 96, and thus output adaptor 82, to assume the maximum angularrunout position.

[0079] Referring to FIG. 8, the adjustment disc assemblies 70 and 72 andassociated adjustment discs 90 and 92 are rotated in relation to eachother so that the “slant” or wedge on respective interfaces complementeach other and the input surface of the assembly is parallel with theoutput surface. This is accomplished by stopping the stop disc 94 untilthe pin 114 couples with the slant disc 90. Thus the output adaptor 82“runs true” to the input rotation axis. The angle of the interface ofthe two slant discs has been exaggerated in the figures for clarity. Theangle is of a dimension that depends on the application of the lathe,but may be on the order of 0.323 degrees. It is noted that because theinput adaptor 66 is solidly mounted to the shaft 68 and its face isperpendicular to the axis of rotation, the adaptor 66 serves as apositioning reference to the slant disc assembly 70. Referring to FIG.9, the slant disc assemblies 70 and 72 are rotated in relation to eachother by stopping the stop disc 96 until the pin 114 couples to theslant disc 90. In this position, the slant angles on the two slant discsadd to each other to cause the output surface of the assembly and theoutput adaptor 82 to display maximum angular runout with the inputrotation axis.

[0080] The runout caused by a misalignment between the vehicle's hubaxis and the axis of the lathe can be corrected without the timeconsuming and inaccurate manual methods of the prior art. Additionaladjustment motors are not necessary. Accurate and automated realignmentis possible when the system is operated in conjunction with ameasurement and control system of the type described below.

[0081] Another implementation incorporates the fundamental features ofthe implementation disclosed above, but permits adjustment with only oneslant disc. The output pivots in one selectable axis only when driven bythe slant disc. In the implementation described above, the compensationvector (explained in more detail with reference to FIGS. 11A and 11B)necessary to adjust the angle of the output adaptor 82 could potentiallyrequire adjustment of two slant discs. The fixed pivoting axis of thisimplementation eliminates this problem by requiring only one adjustment,and, potentially, reduces the time required for shaft alignment.

[0082] Referring to FIG. 10A, an automatic alignment coupling ormechanism 120 occupies the same position of the mechanism 50 shown inFIG. 4. Input adaptor 122 attaches to the rotating shaft of the lathemachine. Shaft 124 is attached to the input adaptor 122 such that theadaptor 122 mounting face is perpendicular to the shaft 124 so thatshaft 124 runs true with the lathe machine axis. A second shaft 126 isplaced over the shaft 124. The rotated position of the second shaft 126relative to shaft 124 is controlled by the stop disc assembly 128. Thestop disc assembly 128 contains a gear train and operates similarly tothe stop disc assemblies 70 and 72. However, in this case, instead ofdriving a slant disc when the stop disc 130 is stopped by anelectromagnetic catch, the second shaft 126 is driven and movesbackwards relative to the shaft 124. Rotary movement of the shaft 126also controls the rotary position of a pivot ring assembly 132 which isfirmly attached to the second shaft 126. An output adaptor 134 ismounted on the shaft 124, held in place by a clamp ring 136, and causedto rotate with the shaft 124 by a drive disc 138.

[0083] A second stop disc assembly 130, including a gear train, ismounted on the second shaft 126 and operates similar to stop discs 94and 96. The output of the gear train drives a single slant disc 140 asshown in FIG. 10C. When stop disc 130 is stopped, the slant disc 140moves backward in relation to shaft 124. The axial force produced by anaxially mounted drawbar 58 (FIG. 4) causes the output adaptor 134,through the pivot ring 132, to assume an angle to the shaft 124depending upon the rotated position of slant disc 140.

[0084] Referring to FIG. 10B, the automatic alignment mechanism may berotated 90 degrees counterclockwise about the input axis of FIG. 10A.The pivot ring 132 does not rest against the stop disc assembly 130 overits entire surface. Rather, there are two bumps diametrically placed onthe face of the pivot ring 132 which rests against the stop discassembly 130. This allows the slant disc 140 to transmit its angle tothe pivot ring 132 but allows the pivot ring 132 to pivot on its fixedaxis pins 142. Thus, once set, the compensation vector for alignmentdoes not change when the slant disc 140 varies the output compensationangle. FIG. 10D shows the pivot ring assembly 132 in more detail.Specifically, by making one of the bumps on the pivot ring 132 a certainamount larger than the other, the pivot ring 132 is made to beperpendicular to the shaft 124 at one extreme position of slant disc 140and to be at the maximum compensation angle at the other extreme. A ½degree variance, for example, is provided between the bumps as shown inFIG. 10D. Similarly, a ½ degree variance between the bumps on slant disc140 is provided as shown in FIG. 10C. Thus, when the slant disc 140 andthe pivot ring 132 are placed against the disc 130 with the ½ degreeface angles complementing each other, a 0 degree runout between theinput and output adaptors is achieved. On the other hand, when the discsare rotated 180 degrees relative to each other, the angles oppose eachother and the runout is 1 degree.

[0085]FIGS. 11A and 11B depict the relationship between the compensationvector, compensation angle, and pivot axis. Generally, two parametersare of importance when aligning the rotating shafts of the lathe andbrake hub. The first parameter, referred to as the compensation vector,is defined by the rotation position at which the lateral runoutdeflection of the brake lathe is the greatest. The second parameter,referred to as the compensation angle, is defined by the angle that theinput adaptor and the output adaptor must assume in relation to eachother to compensate for this lateral runout. The compensation vector andthe compensation angle can be adjusted separately as shown in FIG. 10A.

[0086] In the implementations of FIG. 4 and FIG. 12 (described below),the compensation vector is adjusted by stopping simultaneously the inputdisc and output disc. This does not affect the relative rotationalpositions of the discs and thus does not change the input to outputangle. Rather, adjustment of the compensation vector only changes therotational position at which the disc's angle changing capability iseffective. The compensation angle is adjusted by stopping the outputdisc only, which rotates it in relation to the input disc and thuschanges the input-to-output angle.

[0087] FIGS. 12-16 show another implementation that is similar to thefirst implementation, but differs in that the slant discs are separatedfrom each other and from the input and output adaptors by pin rollerthrust bearings to allow free rotation of these elements under normalaxial pressure. The rotational positioning of the slant discs relativeto each other and to the input and output adaptors is performed byactuating four starwheels which drive the slant discs through geartrains. In addition, forward and reverse positioning capability of theslant discs is provided, which allows a considerable decrease in time tofinal alignment.

[0088] Referring to FIG. 12, an automatic alignment coupling ormechanism 144 occupies the same position of the mechanism 50 shown inFIG. 4. An input adaptor 146 attaches to and is rotationally driven bythe output shaft of the brake lathe. Adaptor 146 contains two starwheels180 and 182 that drive gear trains to position an input slant disc 152,which is described in more detail with reference to FIG. 13A. An adaptorcover 154 serves as a cover for the gearing and as a bearing surfacethat runs perpendicularly true to the shaft 156, which is attached toinput adaptor 146.

[0089] Thrust bearing assembly 158 is placed between input slant disc152 and the bearing surface of adaptor cover 154. This bearing assemblyallows free rotation of the slant disc 152 relative to the input adaptor146 and the attached shaft 156 while automatic alignment mechanism isunder axial pressure in normal operation. Output slant disc 160 isseparated from slant disc 152 by a thrust bearing assembly 162 identicalto thrust bearing assembly 158 to allow output slant disc 160 to freelyrotate under axial pressure. A third thrust bearing assembly 164 isplaced between output slant disc 160 and the output adaptor cover 166,to allow free rotation of the output slant disc 160.

[0090] Output adaptor 168 contains a starwheel and gearing assemblycomparable to that of input adaptor 146. It differs in that it is freeto move to an angle that varies as much as 1 degree, for example, fromperpendicular to the shaft 156 axis. Output adaptor 158 is rotationallycoupled to the shaft 156 by means of a drive arm 170 that is keyed tothe shaft 156.

[0091]FIG. 13B shows the input side of the output adaptor 168 withoutthe starwheel and gears. The drive arm 170 is shown in place with key172 coupling it to the shaft 156. A drive pin 174 is positioned in theoutput adaptor 168 and fits in the slot 176 of the drive arm 170 tocause the output adaptor 168 to rotate with the shaft 156 while allowingthe output adaptor 168 to tip angularly in relation to the shaft 156.

[0092] Referring to FIG. 12, a collar 178 serves as both a bearingsurface for the inside diameter of output adaptor 168 and a shoulder toprevent disassembly of the parts when the automatic alignment mechanismis not operating under axial pressure. A wave washer 153 or the like isplaced between input slant disc 152 and input adaptor 146 to providesome friction so that rotation of output slant disc 160 will not causeunwanted rotation of the input slant disc 152.

[0093] Referring to FIG. 13A, input and output adaptor assembliespreferably include a forward starwheel 180 that is coupled to a gear 184having, for example, 18 teeth. Gear 184 meshes with a gear 186 having,for example, 56 teeth. Gear 186 is coupled to gear 188 having, forexample, 18 teeth. Gear 188 meshes with a ring gear 190 having, forexample, 140 teeth. The ring gear 190 is operably attached to arespective slant disc 152 or 160 as shown in FIG. 12.

[0094] Referring again to FIG. 13A, when the entire automatic alignmentmechanism rotates at 2.05 RPS, for example, in normal operation, thestarwheel 180 can be caused to rotate by catching one or more teeth asthe starwheel 180 passes by a fixed stop mechanism comprising anelectromagnetic catch or the like. Thus, a slant disc can be caused torotate in increments relative to the automatic alignment mechanism. Thereverse starwheel 182 and gear assembly operate similarly to the forwardstarwheel 180 and gear assembly except that an additional gear 192causes the slant disc to rotate in the opposite direction when thestarwheel 182 is rotated.

[0095] Referring to FIG. 14, a starwheel stop mechanism 194 includes atoothed catch member 196 and a magnetic element such as solenoid 198 orthe like. One stop mechanism 194 may be provided to operate inconjunction with the input adaptor 146 and another may be provided tooperate in conjunction with the output adaptor 168. The toothed member196 may contain one or more teeth so as to catch one or more starwheelteeth during each rotation of the automatic alignment mechanism. Notethat the teeth of the member 196 are spaced apart so as to allow time tolift the toothed member between starwheel contact to control the amountof starwheel rotation per rotation of the automatic alignment mechanism.

[0096] As the starwheels on each adaptor 146 and 168 are in line, theaction of the starwheel catch or stop mechanisms have to be timed insynchronism with the rotation of the automatic alignment mechanism sothat only the desired starwheel (i.e., forward starwheel 180 or reversestarwheel 182) is actuated.

[0097] FIGS. 15A-15G show exemplary timing control diagrams for thestarwheel stop mechanism 194. As shown, a hall transducer or the likeproduces a timing pulse that is used as a time reference point.

[0098] Referring to FIG. 16, alignment may be achieved according to aprocedure 300. It is noted that any suitable measurement device could beused in conjunction with the alignment mechanism. Preferably, however,the sensing and measuring device described below operates in conjunctionwith the alignment mechanisms described above. It is also noted thatalthough the alignment process is shown and described in FIG. 16 withreference to the implementation of FIG. 12, the general processalgorithm is applicable to all of the described implementations.Furthermore, the alignment apparatus and process may also beadvantageously used in other practical applications to align twoconcentrically rotating shafts.

[0099] In general, the flow diagram of FIG. 16 shows a sequence of trialand error adjustments wherein an adjustment is initially made bystopping a starwheel on one of the adaptors and measuring the change inthe runout or alignment. If the runout improves, an additionaladjustment is ordered in the same direction. If the alignment worsens,an adjustment in the opposite direction is ordered. This process isrepeated until the alignment is corrected to within specifications andthe lathe shaft and hub axes are aligned. Two distinct periods ofadjustment are employed. In a first cycle, large adjustments are made inthe orientation of slant discs 152 and 160 to more significantly changethe alignment of the shaft and hub axes to correct runout. Oncealignment reaches a predetermined low level, finer adjustments are madeto correct runout to within specified tolerances.

[0100] The runout correction process begins with initialization ofseveral variables (step 302). First, the stop level of stop mechanism194 is set to three actuations of the starwheels. This provides thelarge movements of slant discs 152 and 160 at the beginning of theadjustment cycle. In addition, several internal counts and limits areinitialized including flag Z, flag D, and a try counter. Also, theinitial specification value is set to represent an acceptable level ofrunout. Typically, this value is set to be in the order of 0.001 inches.The try counter operates when runout drops to a “Min” value. Thiscounter causes the value of “Spec” to increase after the systemunsuccessfully tries to reach the present “Spec” runout value aprogrammed number of tries or cycles. This prevents the system fromtrying to forever reach a runout value that is impossible given thecircumstances.

[0101] After initializing the variables, an initial evaluation of therunout is made and stored as R-pres (step 303), which is representativeof a base value of the runout. The measured runout then is compared witha runout measurement that conforms to specification (step 304), which,as noted above, is typically on the order of 0.001 inches. If the runoutis less than 0.001 inches, the runout is determined to fall withinspecified tolerances (“Spec”) and no further compensation is required.In this case, a “Ready to Cut” light or similar mechanism is actuated toindicate that compensation is complete (step 305) and the procedure ends(step 306).

[0102] If further compensation is required, the value of R-pres iscopied into the memory location of R-last (step 307). Next, if R-presdoes not exceed a predetermined “Min” level (step 308), the stopmechanism 196 is set to stop one tooth of the starwheel 180 or 182 perrevolution (step 309), a try count is incremented (step 310), and thetry count is evaluated to determine whether it is at a limit (step 311).

[0103] If the try count is at its limit, the runout “Spec” limit israised (step 312) and the try count is reset to 0 (step 313). The higher“Spec” limit usually is a value that is still acceptable but lesspreferred than the original “Spec” limit (e.g. 0.001 inch). For example,a higher “Spec” of 0.003 inches is acceptable.

[0104] After resetting the try count (step 313), determining that thetry count is not at the limit (step 311), or determining that R-pres isnot less than the minimum (step 308), the flag Z is tested to determineif starwheel actuation has run in both directions (step 314). That is,whether both output 180 (forward) and 182 (reverse) starwheels have beenactivated. If the Z flag has been toggled twice, then flag D is toggled(step 315).

[0105] After toggling flag D (step 315) or determining that the Z flaghas not been toggled twice (step 314), the state of flag D is determined(step 316). If D equals 0, then the output only starwheel is actuated tochange the compensation angle of the system (step 317). If D equals 1,both the output and input starwheels are actuated to change thecompensation vector of the system (step 318).

[0106] The system then waits for one of two revolutions of the lathebefore proceeding (step 319) to allow transients introduced by the laststarwheel adjustment to dissipate. The number of revolutions depends onthe ability of the rotational motion sensor to track changes in therotational motion.

[0107] Next, the runout is measured again and stored as R-pres (step320). If the new runout is less than Spec (e.g., 0.001 or 0.003 inches)(step 321), the adjustment process is complete and the system proceedswith steps 305 and 306.

[0108] R-pres then is compared to R-last, the runout from the lastmeasurement (step 322). If R-pres is not less than R-last, then flag Zis toggled to cause motion in the opposite direction (step 323). Aftertoggling flag Z (step 323) or determining that R-pres is less thanR-last (step 322), the system sets R-last equal to R-pres (step 307) andproceeds as discussed above.

[0109] In this manner, the system employs a trial and error approach toreducing runout. As long as the runout continues to decrease, additionalactuations of the same starwheel occur. However, if runout worsens, theopposite starwheel is actuated to begin to correct the runout. If thisforward and reverse cycle does not improve the runout, the compensationvector is adjusted by moving both of the input and output adjustmentdiscs. A microprocessor and suitable circuitry controls the operation ofthe present invention as described below.

[0110] The alignment adjustment system is a substantial improvement overprior art devices and techniques. Once the appropriate sensor andmeasuring system is properly secured, the automatic alignment systemprovides for mechanical compensation of the total lateral runout presentin the disc brake assembly. Specifically, the alignment system adjuststhe alignment of the brake lathe component with respect to a vehicle hubto compensate for lateral runout. This, in turn, ensures that thecutting head 36 is placed perpendicular to the rotation axis of the hub44.

[0111] Referring to FIGS. 17 and 18, a brake lathe assembly is coupledto a wheel axle through an automatic alignment mechanism of the typeshown and described above. The lathe tools are shown positioned at theend of the brake assembly mechanism arm and arranged to move from thecenter of the brake disc toward the outside while the drive motor causesthe wheel and brake disc to rotate as described above. The solid linesshow the mechanism position when the wheel axis and the lathe axis arein alignment. The lathe tools cut the disc surfaces smoothly under theseconditions.

[0112] However, when runout is present, as shown in FIG. 17, the lathewill rotate back and forth when in use. The dotted lines show thewobbling of the lathe mechanism when the wheel axis and the lathe axisare misaligned (in the drawing the runout is greatly exaggerated).Wobbling of the lathe mechanism and tools will cut the brake disclateral runout into the rotor, which is unacceptable. At the “X” point,the mechanism changes its position not only linearly but also in arotational sense perpendicular to the drive axis. That is, the angle ofthe mechanism changes cyclically as the wheel rotates.

[0113] The sensing devices of the runout sensing and control mechanismare placed at this X point to optimize measurement sensitivity. Thesensing devices may be positioned such that the internal rotor axis of adevice including such an axis is perpendicular to the lathe drive axis.

[0114] Referring to FIG. 18, another misalignment mode can occur whenthe wheel axis and the lathe axis are in misalignment. This is referredto as off-center misalignment. With off-center misalignment, the motionof the lathe mechanism includes only linear components so that noangular runout occurs and no rotational motion perpendicular to thedrive axis occurs. This runout motion does not detract significantlyfrom the smooth cutting of the brake disc surface and can be allowed.For this reason, the sensing device only needs to sense the rotationalcomponents impressed upon its housing, and may reject all linear motion.

[0115] A number of different sensing configurations can be used as apart of the runout sensing and control mechanism. For example, a rotaryaccelerometer may be employed as the runout detector, in which case twooperating modes are employed. In a first mode, the natural frequency ofresonant motion of the rotor transducer is configured (as explainedbelow) to be about 1.5 times the frequency of lathe rotation. Thisconfiguration permits the accelerometer to rapidly follow changes inrunout and, therefore, provides rapid alignment, due to damping inherentin the frequency differential. However, the runout sensitivity of thesystem is less than half that of the second mode.

[0116] In the second mode, the natural frequency of resonant motion ofthe rotor transducer is configured to be below the frequency of latherotation. This provides increased sensitivity to runout and helps tosuppress harmonics in the runout motion which can cause alignmentuncertainty. However, this mode is slower in following changes inrunout, which may slow alignment as compared to the first mode. In anyevent, the natural frequency of resonant motion should never be placedat the frequency of lathe rotation because operating in resonance withthe lathe results in an unnatural buildup of rotor-transducer motionwhich doesn't allow the accelerometer output to immediately follow therunout magnitude and seriously slows the alignment process.

[0117] Independent of the operation mode, several considerations arerelevant in implementing the accelerometer. First, the accelerometerrotor should be completely balanced to insure measurement of rotationalaccelerations while rejecting linear accelerations. Second, the rotationof the rotor should be physically limited such that rotation only occurswithin the sensitive area of the transducer. Finally, the naturalfrequency of resonant motion of the rotor-transducer should beconfigured to operate in either of the modes discussed above. In thisregard, the natural frequency depends on several variables including themass of the rotor, the diameter of the rotor, and characteristics of aspring element.

[0118] An accelerometer embodiment using a piezo-electric element as asensor is well suited to operate under conditions in which the naturalfrequency of resonant motion is about 1.5 times the frequency of latherotation. Some force is required to bend the element, which tends tocause a high spring rate. Other transducer approaches, which generallyemploy non-contact devices, permit the spring rate to be controlled byspring selection. As such, these approaches are well suited to eithermode one or mode two operation.

[0119]FIGS. 19A and 19B show a rotary accelerometer sensor 400. Sensor400 includes a housing 402 that encloses a rotor 404 mounted forrotation on bearings 406 and 408. The rotor 404 is carefully balanced sothat all accelerations except rotational acceleration cause no rotationof the rotor 404. Rotation of the rotor 404 is sensed by a piezoelectric element 410 mounted between the housing 402 and the rotor 404.Element 410 is bent by any rotation of the rotor 404 to produce avoltage proportional to the magnitude of bending. The piezo electricelement 410 is mounted in a slot 412 in the rotor 404 to limit rotationof the rotor 404 and thereby protect the piezo electric element 410.

[0120] The piezo electric element 410 and the rotor 404 operate as aspring and mass system having a natural frequency of resonant motion. Inthis system, the rotor 404 constitutes the mass and the piezo electricelement 410 constitutes the spring. The system operates in mode one, inthat the rotor mass and diameter, and the piezo spring constant, areadjusted to obtain a resonant frequency on the order of 1.5 times thefrequency of lathe rotation.

[0121] The rotor 404 also should be suitably damped to minimize thesettling time. This can be achieved by filling the housing 402 with aviscous fluid and sealing the housing with a cover. Alternatively,damping can be provided by using a clinging viscous material in thebearings 406 and 408. Other damping techniques may also be employed.

[0122] The piezo electric element 410 produces a voltage having amagnitude proportional to the magnitude of the angular runout. Thiscontrol signal is supplied to a control system.

[0123] The sensing device may employ alternative transducing elements toprovide the control signal. For example, as shown in FIG. 20, thesensing device may employ an accelerometer with a tuned coil oscillator.The spring component of this system includes a wire (preferably music orpiano wire) 425 that is attached to a body 427 and rotor 429 as shown.The wire may be attached by any suitable means, such as, for example,brackets 431. As previously noted, the natural frequency of resonantmotion of the rotor-transducer depends on the mass and diameter of therotor and the spring characteristics of the wire. When using a musicwire 425 to control frequency as shown, the diameter of the wire and thetension in the wire 244 are manipulated to vary the frequency. Forexample, to achieve a natural frequency or resonant motion of therotor-transducer that is below the frequency of lathe rotation, adiameter in the range of approximately 9-10 thousandths of an inch isused and the wire tension is configured to be relatively loose. On theother hand, to achieve a natural frequency of resonant motion of therotor-transducer that is about 1.5 times the frequency of latherotation, a diameter on the order of approximately 16 thousandths of aninch is used and the wire tension is configured to be relatively tight.

[0124] A ferrite or the like disc 433 is placed in the periphery of therotor 429 adjacent to a housing-mounted coil 435 which serves as theinductor of an oscillator circuit 437. When the rotor 429 turns, theferrite disc 433 moves in relation to the coil 435, causing a change inthe inductance of the coil and a corresponding change in the frequencyof oscillation. A discriminator 439 converts the change in frequency ofoscillation to a varying DC voltage. This varying voltage reflects therotation of the accelerometer housing 427. The signal is then forwardedto the control system.

[0125] As previously noted, it is important to configure the rotor suchthat it is balanced. To limit the rotation of the rotor such thatrotation only occurs within the sensitive area of the transducer, acounterbore 441 is provided to cooperate with a pin 443 to limit rotorrotation as appropriate. Other limiting means may also be used.

[0126] Referring to FIG. 21, an accelerometer with a magnet 450 and ahall effect transducer 452 also may be used. In this configuration, aleaf spring 454 has a spring rate which, in combination with the inertiaof the rotor 456, provides a resonant frequency about 1.5 times therotational rate of the brake lathe shaft (i.e. operation in mode one).Alternatively, the accelerometer could be configured to operate in modeone or two using a music wire as described above.

[0127] The magnet 450 is placed in the periphery of the rotor 456. Thehall effect transducer 452 has a linear characteristic and is placed inthe housing 458 adjacent to the magnet 450 such that rotary motion ofthe rotor is reflected in the output voltage of the hall effecttransducer 452. The magnitude of the AC voltage at the output of thehall effect transducer 452 is a reflection of the rotary motion of theaccelerometer housing 458 that is attached to the lathe, preferably atthe position identified with reference to FIGS. 17 and 18. The resultingsignal is forwarded to a control system.

[0128] In yet another implementation, as shown in FIGS. 22 and 22A, thesensing element may includes an accelerometer with an infraredgenerator. A leaf spring 475 has a spring constant which, in combinationwith the inertia of a rotor 477, provides a resonant frequency about 1.5times the rotational rate of the brake lathe shaft. Again, thisaccelerometer could alternatively be configured to operate in mode oneor two using a music wire as described above. An infrared generatordiode 479 is placed facing an infrared detector diode 481 on the housing483 near the periphery of the rotor 477.

[0129] A shutter 485 is attached to the rotor 477 and projects betweenthe IR generator 479 and IR detector 481 such that rotary motion of therotor 477 varies the amount of radiant energy transferred, causing thevoltage produced by the IR detector 481 to reflect the magnitude ofrotation of the housing 483 (i.e., the runout of the disc coupling). Thesignal then is forwarded to the control system.

[0130] Referring to FIGS. 23 and 23A, yet another implementation employsan infrared sensor and detector as described above. The rotor 500 has amagnet 502, such as a Neo Iron Boron type magnet available fromJobmaster as Part No. NE0270200N, embedded in its upper face. Alinearly-adjustable tapped block 504 is mounted on the underside of thecover 506 of the accelerometer housing 508. A permeable screw 510threads into the block 504 and is positioned so that, with the covermounted on the housing, the end of the screw sits just above the magnet502.

[0131] The block 504 may be adjusted using screws 512 in slots 514 toposition the rotor 500 by magnetic attraction. This permits positioningof the rotor so that the shutter 516 interrupts infrared energy in aninfrared sensor assembly 518 using a generator and detector as describedabove with reference FIGS. 22 and 22A to provide a desired steady stateDC output voltage.

[0132] Turning the permeable screw 510 to move it toward the magnet 502provides an increase in magnetic attraction and consequent increases inthe spring constant and the natural frequency at which the rotor rings.Moving the screw away from the magnet 502 has the opposite effect.

[0133] With good bearings, the rotor has low loss such that rotary moderinging occurs for several seconds after the rotor is actuated. This isnot desirable since it impedes the accelerometers ability to follow achanging actuating force.

[0134] Ringing is reduced by damping provided by a ferro fluid 520, suchas is available from Ferrofluidics Corporation. A ferro fluid is anoil-based fluid with a suspension of microscopic permeable particlesthat cause the fluid to cling to a magnet.

[0135] The permeable screw, the ferro fluid, and the magnet are arrangedin a plastic cup 522 in the periphery of the rotor. A drop of ferrofluid 520 on the magnet 502 clings to the interface between the magnetand the permeable screw. The fluid is of sufficient viscosity to dampthe rotor to reduce ringing time by a factor of three. To preventunwanted interaction between the fluid and the surface of the magnet,the magnet may be covered by a piece of Teflon tape to seal the surfaceof the magnet.

[0136] The viscosity of the ferro fluid is temperature sensitive. Thismeans that system performance may vary with varying temperature.

[0137] Referring to FIGS. 24 and 24A, temperature sensitivity may bereduced by heating the fluid. A thermally conductive block 525, whichmay be metal, is used for electrical heating. Block 525 is larger thanthe unheated block 504 to allow for a slot into which a positivetemperature coefficient (PTC) resistance element 527 may be potted usingthermally conductive epoxy. The PTC element 527 is supplied by wires 529from a fixed DC voltage source.

[0138] To thermally isolate the block 525 from the cover 506, aninsulating pad 531 is placed between the two. The block 525 is held inplace by nylon screws 533 to further thermally isolate the block.

[0139] In yet another variation, the accelerometer is replaced by anangular rate sensor that employs a pair of micromachined tuning forks.Rotation of the sensor induces a Coriolis effect that causes adifference in the output of the two forks. The difference is reflectedin the output of the sensor, and provides an indication of the rate ofrotation. Such a sensor is available from BEI Systron Donner InertialDivision Sensors and Systems Company of Concord, Calif. as part numberAQRS-00064-109N.

[0140] Referring to FIG. 25, the runout sensing and control mechanismfurther includes a control circuit 600. A transducer 602 may beimplemented using an accelerometer or angular rate sensor as describedabove to evaluate the rotational acceleration of the lathe. Becauselateral runout manifests itself in varying rotational motion imparted tothe lathe, any sensor arrangement capable of producing an accuratequalitative measure of rotational acceleration may be used. Thefollowing discussion assumes that the transducer produces an alternatingcurrent signal having a magnitude that varies with the degree ofrotational motion.

[0141] The output of transducer 602 is fed to an amplifier 604 and thento a rectifier 606. Because runout produces a cyclical motion in thelathe, the signal produced by transducer 602 is sinusoidal in nature.However, other wave forms could resonate at lower runout. Afteramplification by amplifier 604 and rectification by full wave rectifier606, the peak runout signal is fed to an integrator 608 that is resetduring each lathe rotation cycle. The signal is then sent to a sampleand hold circuit 610.

[0142] A hall pickup timer 612 produces a synchronization signal. Thissignal causes a switch 614 to transition to discharge a capacitor 616 toreset the integrator 608. The synchronization signal also causes aswitch 618 to transition to store the output value of the integrator inthe sample and hold circuit 610 prior to discharging the capacitor.

[0143] The output of the sample and hold circuit 610 is transmitted toan A/D converter 620 which samples the output and produces a digitalrepresentation of the voltage level. The output of the AID converter 620is provided to a latch 622 and a microprocessor 624. The microprocessor624 also receives the output of latch 622. Latch 622 is a conventionalsample and hold latch and is clocked just prior to the time A/Dconverter 620 presents a new sample. In this manner, both the currentsample taken by A/D converter 620 and the last sample taken by A/Dconverter 620 are available to microprocessor 624. Amplifiers 626 and628 are provided at the output of microprocessor 624 to drive the stopmechanism(s).

[0144] Taken in conjunction with the algorithm set forth in FIG. 16,microprocessor 624 is thus provided with a stream of samples of therunout of the rotor under consideration, together with a samplerepresenting the last historical value of the runout. In this manner,the microprocessor implements the trial and error approach describedabove with respect to FIG. 16.

[0145] FIGS. 26-31 illustrate another implementation of the runoutadjustment mechanism. This implementation is similar to theimplementation of FIG. 12 in that the rotational positioning of theslant discs relative to each other and to the input and output adaptorsis performed by actuating four starwheels, or stop discs, to drive geartrains that then drive the slant discs. In this implementation, however,the four starwheels are all aligned in the same plane. With thisarrangement, only one stop mechanism is needed to actuate thestarwheels, with the correct starwheel being selected through timedactuation of the stop mechanism.

[0146] The runout adjustment mechanism may be totally enclosed, so as toprevent contamination by metal chips produced as a result of the latheoperation. A separate cover is not required. The stop mechanism may bemounted adjacent to the runout adjusting mechanism and may be providedwith its own cover to prevent contamination by lathe chips.

[0147] The single-plane implementation of FIGS. 26-31 uses a reducednumber of components and, accordingly, is less expensive to manufacturethan the implementation of FIG. 12. The single-plane implementation alsois “stiffer” because it does not require the partially hollow input andoutput adaptors of the implementation of FIG. 12 since gearing may bepositioned at the periphery of the mechanism.

[0148] Referring to FIGS. 26 and 27, an alignment mechanism 700 occupiesthe same position as the mechanism 144 of the implementation of FIG. 12.An input adaptor 702 is attached to and is rotationally driven by theoutput shaft 704 of a brake lathe. Input adaptor 702 includes fourstarwheels 706-712 which drive gear trains to position two slant discs,as described in more detail with reference to FIG. 28.

[0149] A stop mechanism assembly 714 is mounted on the bearing cap 716of the brake lathe by means of a mounting yoke 718. The stop mechanismdepicted in FIGS. 28 and 29 includes a solenoid 720 coupled by a link722 to an actuator arm 724 attached to a starwheel stopper 726. A coilspring 728 serves to open the solenoid core and retract the stopper 726when the solenoid 720 is not powered. A stop pad 730 serves to cushionthe return of actuator arm 724 when the solenoid 720 is de-energized. Inother implementations, the stop mechanism 714 may employ devices otherthan a solenoid.

[0150] When the stop mechanism 714 is activated, the actuator arm 724forces the starwheel stopper 726 against the periphery of the alignmentmechanism 700 and into the path of the four starwheels 706-712. A syncmagnet 732 carried by the rotating alignment mechanism 700 passes by ahall detector 734 once each revolution. The hall detector 734 providesan output that serves as a timing signal for electronic control of thestop mechanism 714.

[0151] Referring to FIG. 28, the alignment mechanism 700 includes anoutput adaptor support 736 attached to the input adaptor 702. A pin 738projects from a peripheral surface of the output adaptor support 736 andserves to rotationally couple an output adaptor 740 to the input adaptor702 so that the output adaptor 740 rotates with the brake lathe shaft704. A collar 742 serves to hold the output adaptor 740 on the outputadaptor support 736 while allowing the output adaptor 740 to tip at upto a desired angular limit (for example +/−1 degree) from perpendicularto the rotational axis.

[0152] The periphery of the output adaptor 740 is grooved to accept arubber “O” ring 744. A seal ring 746 attached to the input adaptor 702cooperates with the “O” ring 744 to seal the interior of the mechanismagainst contamination.

[0153] Slant discs 748 and 750 serve to vary the angle between the inputadaptor 702 mounting surface and the output adaptor 740 mountingsurface. Slant discs 748 and 750, which have gear teeth on theirrespective peripheries, are mounted between the input adaptor 702 andthe output adaptor 740. Three sets of pin roller thrust bearings 752-756separate the slant discs 748 and 750 from each other and from the inputadaptor 702 and the output adaptor 740. Under normal axial pressure, thethrust bearings 752-756 allow the slant discs 748 and 750 to rotatefreely in relation to each other and in relation to the input adaptor702 and output adaptor 740.

[0154] The mounting surface of the input adaptor 702 and the mountingsurface of the output adaptor 740 are caused to be parallel when theequally angled faces of the slant discs 748 and 750 are rotated to aposition in which they complement each other. The mounting surfaces areoffset from parallel when the equally angled faces of the slant discs748 and 750 are rotated to a position in which they oppose each other.

[0155] Four starwheels 706-712 attached to gears 758-764 by shafts766-772 facilitate rotational control of the slant discs 748 and 750 inrelation to each other and in relation to the input adaptor 734 and theoutput adaptor 740.

[0156]FIG. 29 shows the relative locations of the starwheels 706-712 andthe sync magnet 732. Also shown are the brackets 774 and 776 that claspthe shaft alignment mechanism to the brake lathe output shaft 704.Shafts rotationally couple the starwheels 706-712 to corresponding gears758-764. Gears 758 and 760 directly engage the teeth on the periphery ofthe slant discs 748 and 750, respectively. This arrangement causes slantdiscs 748 and 750 to rotate with the rotation of the respectivestarwheels 706 and 708. Gears 762 and 764 engage reverse gears 778 and780, respectively, which engage the teeth on the periphery of slantdiscs 748 and 750, respectively. Reverse gears 778 and 780 serve toreverse the rotational direction of slant discs 748 and 750 whenstarwheels 710 and 712 are rotated.

[0157] Each starwheel serves a distinct function. Starwheel 706, whichmay be labelled the “A Disc Forward” starwheel, is rotationally coupledto gear 758 by shaft 768. Gear 758 engages the teeth on the periphery ofslant disc 748. Thus, when one of the teeth of starwheel 706 is stoppedor caught by the stopper 726, slant disc 748 (the “A Disc”) rotates in aforward direction relative to the alignment mechanism 700.

[0158] Starwheel 708, which may be labelled the “B Disc ForwardStarwheel” works in a similar fashion as starwheel 706 described above,except that when starwheel 708 is engaged, slant disc 750 (the “B Disc”)rotates in a forward direction.

[0159] Starwheel 710 may be labelled the “A Disc Reverse Starwheel.”Starwheel 710 is rotationally coupled to gear 762 by shaft 770. Gear 762engages reverse gear 778, which engages the teeth along the periphery ofslant disc 748. Thus, when one of the teeth of starwheel 710 is caughtby the stopper 726, gear 778 reverses the rotational direction, andslant disc 748 (the “A Disc”) rotates in a reverse direction relative tothe alignment mechanism 700.

[0160] Starwheel 712, which may be labelled the “B Disc ReverseStarwheel” works in a similar fashion as starwheel 710 described above,except that when starwheel 712 is engaged, slant disc 750 (the “B Disc”)rotates in a reverse direction.

[0161]FIG. 30 illustrates actuation timing for adjustment of thecompensation angle using the single-plane mechanism. Adjustment of thecompensation angle may be achieved through incremental rotation ofeither of the slant discs 748 or 750 in either forward or reversedirections. With the single-plane implementation, control of theactuation is achieved exclusively through timing of the single stopper726.

[0162] The concentric circles 782-788 of FIG. 30 are calibrated in time.Time zero is defined as the time, in a given revolution, at which thesync magnet passes the hall detector, as described with reference toFIGS. 26 and 27. The concentric circles in FIG. 30 show the elapsed timein milliseconds from time zero to the calibrated point, when thealignment mechanism 700 is rotating normally at 2.054 revolutions persecond. The times indicated are approximate and may be varied to achievea desired adjustment operation. The solid line of each of circles782-788 indicates the stopper 726 actuation period. Each of circles782-788 represents the actuation timing for a particular change in thecompensation angle.

[0163] In the diagram of FIG. 30, the stopper 726 includes two prongs.The stopper prongs are separated such that, at the rotation rate of thealignment mechanism 700, forty milliseconds will elapse from the time astarwheel passes the first stopper prong to the time the same starwheelpasses the second stopper prong. Thus, the stopper can be actuated intime to catch a first tooth of a selected one of the starwheels 706-712with the first stopper prong, while leaving 40 milliseconds during whichthe stopper may be retracted so that the second stopper prong does notcontact a second tooth of the selected starwheel. The stopper 726 may beconfigured with more stopper prongs as needed to facilitate the desiredstarwheel actuation.

[0164] The number of teeth of a selected starwheel caught during arevolution of the alignment mechanism 700 can be programmed. Preferably,when the alignment runout is large, the program calls speeds adjustmentby calling for two teeth of the selected starwheel to be caught duringeach revolution. This may be referred to as dual-stop actuation. As therunout approaches zero, one tooth is caught per revolution to allowfiner adjustment. This may be referred to as single-stop actuation.

[0165] Circle 782 represents a “Forward-Angle, Single-Stop” actuation.The actuation period is indicated by the solid portion of circle 782.Thus, to adjust the compensation angle in a forward direction, thestopper 728 may be actuated for 45 milliseconds beginning 122milliseconds after time zero. During this period, one tooth of starwheel706 (the “A Disc Forward Starwheel) is caught by the stopper 726. As aresult, slant disc 748 (the “A Disc”) rotates forward by a correspondingamount relative to the alignment mechanism 700, as described above.

[0166] Circle 784 represents a “Forward-Angle, Dual-Stop” actuation.During this actuation, two teeth of starwheel 706 are caught, and slantdisc 748 rotates forward by a corresponding amount relative to thealignment mechanism. The amount of slant disc 748 rotation in thisactuation is larger than that of the “Forward Angle, Single Stop”actuation because two teeth of starwheel 706 are caught instead of one.

[0167] Circles 786 and 788 represent the “Reverse-Angle, Single-Stop”and “Reverse-Angle, Dual-Stop” actuation periods, respectively. Thereverse actuations are similar to the forward-angle actuations exceptthat starwheel 710 (the “Reverse A Disc Starwheel”) is engaged so thatslant disc 748 rotates in a reverse direction relative to the alignmentmechanism 700.

[0168]FIG. 31 shows the actuation timing for adjustment of thecompensation vector using the single-plane mechanism. As in FIG. 30, theconcentric circles 790-796 in FIG. 31 are calibrated and show theelapsed time in milliseconds from time zero to the calibrated point withthe alignment mechanism 700 rotating normally at 2.054 revolutions persecond. Each of circles 790-796 represents the actuation timing for aparticular change in the compensation vector. The times indicated areapproximate and may be varied to achieve a desired adjustment operation.

[0169] Adjustment of the compensation vector may be achieved throughincremental rotation of both slant discs 748 and 750 by equal amounts inthe same direction (either forward or reverse). The compensation vectorchanges as the slant discs 748 and 750 rotate relative to the alignmentmechanism 700. However, the compensation angle remains the same. Becauseboth slant discs 748 and 750 are rotated by the same amount in the samedirection. Depending on the amount of adjustment needed, the actuationmay be single-stop or dual-stop.

[0170] Circle 790 represents a “Forward-Vector, Single-Stop” actuation.This process involves actuating the stopper 726 for a period ofapproximately 45 milliseconds beginning at time zero, and again for 45milliseconds beginning 122 milliseconds after time zero, as indicated bythe solid portion of circle 790. During this process, the stopper 726first catches a single tooth of starwheel 712, which causes slant disc748 to rotate forward, and then catches a single tooth of starwheel 706,which causes slant disc 750 to rotate forward by the same amount.

[0171] Circle 792 represents a “Forward-Vector, Dual-Stop” actuation. Inthis process, the stopper 726 is actuated for a period of 192milliseconds beginning at time zero. During this period, two teeth oneach of starwheels 712 and 706 are caught and the slant discs 748 and750 are caused to rotate forward by a corresponding amount.

[0172] Because two teeth are caught on each of starwheels 712 and 706,the slant discs 748 and 750 rotate by a larger amount and thecompensation vector is adjusted by a larger degree than in the“Forward-Vector, Single-Stop” actuation.

[0173] Circles 794 and 796 represent “Reverse-Vector, Single-Stop” and“Reverse-Vector, Dual-Stop” actuations, respectively. These actuationprocesses are similar to the forward-vector actuations, but differ inthat starwheels 708 and 710 are engaged instead of starwheels 706 and712, so that slant discs 748 and 750 are caused to rotate in a reversedirection relative to the alignment mechanism 700.

[0174] Without attempting to set forth all of the desirable features ofthe instant on-car disc brake lathe with automatic alignment system, atleast some of the major advantages include providing an on-car discbrake lathe having an automated alignment assembly 50 that includes apair of adjustment disc assemblies that are positioned between an inputadaptor 66, 122, 146 and an output adaptor 78, 134, 168. Each of theadjustment disc assemblies includes an adjustment disc 90, 92, 140, 152,160 and associated stop disc. An electromagnetic catch 98, 100 or thelike is operably associated with each of the stop discs 94, 96 andoperates in response to a control signal issued from a control system.When the rotation of one of the stop discs is stopped, rotationalmovement of the lathe drive shaft is transferred, through appropriategearing, to a respective adjustment disc to change the relative positionof the lathe drive axis and the vehicle hub axis.

[0175] The control algorithm and alignment process may include a seriesof trial and error adjustment inquiries to compensate for runout. TheHall signal serves as a timing signal. As the lathe rotates, the runoutlevel is evaluated. If the runout level is within the “Spec” limit,normally 0.001 inches, the alignment goes to the “Ready to Cut” state,the corresponding light is illuminated, and the program ends. If therunout is above the “Spec” limit, an actuation of the output forwardstarwheel is ordered. The runout is evaluated and if lower than theprevious runout, added actuations of the same starwheel are ordereduntil an actuation causes the runout to increase. At this point, if therunout is still above the “Spec” limit, an actuation of the outputreverse starwheel is ordered. If the resulting runout is lower, furthersuch actuations are ordered until an actuation causes the runout toincrease. The previous two actions adjusts the “compensation angle.” Atthis point, if the runout is still above the “Spec” limit, a tandemactuation of both the output and the input forward starwheels isordered. This action adjusts the “compensation vector.” The runout isevaluated and if lower than the previous runout, further tandemactuations of the output and input forward starwheels are ordered untilan actuation causes the runout to increase.

[0176] At this point, if the runout is still above the “Spec”, a tandemactuation of the output and input reverse starwheels is ordered. Therunout is evaluated and if lower than the previous runout, further suchactuations are ordered. If an actuation causes a runout increase, and ifthe runout is still above the “Spec” limit, the starwheel actuationsrevert to the output starwheels only mode again as described previously.This trial and error actuation sequence continues as described aboveuntil the runout is reduced to the “Spec” limit, where the “Ready toCut” light is illuminated and the program ends.

[0177] A count is kept of the number of tries to reach the “Spec” runoutlevel. When a preset number of tries is exceeded, the acceptance levelis raised to about 0.003 inches. If the runout is within this level, the“Ready to Cut” light is illuminated and the program ends. If this newhigher runout level is not reached within a preset number of tries, an“Out of Spec” light is illuminated and the program ends. The operator isdirected to check the lathe coupling to the brake disc hub, to check forbad wheel bearings, to correct the problem, and to try the alignmentcycle again.

[0178] Other embodiments are within the scope of the following claims.For example, referring to FIGS. 32 and 33, instead of using slant discsto adjust the orientation of the input and output adaptors, a joint 800including a ball 802 and a socket 804 may be used. An extension 806attached to the ball 802 is connected to a platform 808 attached to thesocket 804 by three arms 810. The length of the arms can be adjusted tocontrol the orientation of the extension relative to the platform.

[0179] In addition, referring to FIGS. 34 and 35, an adaptor 850 havingfour servo-controlled extenders 852 may be employed. A distance to whicheach extender 852 extends from a surface 854 of the adaptor 850 may becontrolled to control the orientation of the adaptor 850 to acorresponding adaptor 856.

What is claimed is:
 1. An on-car disc brake lathe system for resurfacinga brake disc of a vehicle brake assembly, the brake lathe comprising alathe body with a driving motor, a cutting head operably attached to thelathe body, and a drive shaft, the on-car brake lathe system beingfurther defined by an alignment system including: an electroniccontroller; an input adaptor configured to rotate with the drive shaft;an output adaptor configured to rotate with the drive shaft; at leastone adjustment disc positioned between the input adaptor and the outputadaptor, wherein an axial alignment of the input adaptor relative to theoutput adaptor may be varied based on a rotational orientation of theadjustment disc; and an adjustment mechanism configured to change therotational orientation of the adjustment disc in response to commandsfrom the electronic controller.
 2. The on-car disc brake lathe system ofclaim 1 wherein the adjustment mechanism comprises a stop disc operablein a first state to follow the rotation of the drive shaft and operablein a second state to rotate relative to the rotation of the drive shaftto change the rotational orientation of the adjustment disc.
 3. Theon-car disc brake lathe system of claim 2 wherein the adjustmentmechanism further comprises a stop mechanism associated with the stopdisc and operable to move between a first position in which the stopdisc operates in the first state and a second position in which the stopdisc is caused to operate in the second state.
 4. The on-car disc brakelathe system of claim 3 wherein: the at least one stop disc comprises apair of stop discs, the first stop disc operates in the first state whenthe stop mechanism is in the first position, operates in the secondstate when the stop mechanism is in the second position at a first time,and operates in the first state when the stop mechanism is in the secondposition at a second time different from the first time, and the secondstop disc operates in the first state when the stop mechanism is in thefirst position and when the stop mechanism is in the second position atthe first time, and operates in the second state when the stop mechanismis in the second position at the second time.
 5. The on-car disc brakelathe system of claim 1 further comprising a second adjustment discpositioned between the input adaptor and the output adaptor, wherein theaxial alignment of the input adaptor relative to the output adaptor maybe varied based on the rotational orientation of the adjustment discsrelative to each other.
 6. The on-car disc brake lathe system of claim 5wherein: the adjustment mechanism comprises a first stop disc associatedwith the first adjustment disc and a second stop disc associated withthe second adjustment disc; and each stop disc is operable in a firststate to follow the rotation of the drive shaft and operable in a secondstate to rotate relative to the rotation of the drive shaft to changethe rotational orientation of the associated adjustment disc.
 7. Theon-car disc brake lathe system of claim 6 wherein the adjustmentmechanism further comprises a stop mechanism associated with the stopdiscs.
 8. The on-car disc brake lathe system of claim 7 wherein: thefirst stop disc operates in the first state when the stop mechanism isin the first position, operates in the second state when the stopmechanism is in the second position at a first time, and operates in thefirst state when the stop mechanism is in the second position at asecond time different from the first time, and the second stop discoperates in the first state when the stop mechanism is in the firstposition and when the stop mechanism is in the second position at thefirst time, and operates in the second state when the stop mechanism isin the second position at the second time.
 9. The on-car disc brakelathe system of claim 8 wherein: the adjustment mechanism comprises athird stop disc associated with the first adjustment disc and a fourthstop disc associated with the second adjustment disc; and each stop discis operable in a first state to follow the rotation of the drive shaftand operable in a second state to rotate relative to the rotation of thedrive shaft to change the rotational orientation of the associatedadjustment disc.
 10. The on-car disc brake lathe system of claim 9wherein: the third stop disc operates in the first state when the stopmechanism is in the first position and when the stop mechanism is in thesecond position at the first and second times, operates in the secondstate when the stop mechanism is in the second position at a third timedifferent from the first and second times, and operates in the firststate when the stop mechanism is in the second position at a fourth timedifferent from the first, second, and third times, and the fourth stopdisc operates in the first state when the stop mechanism is in the firstposition and when the stop mechanism is in the second position at thefirst, second and third times, and operates in the second state when thestop mechanism is in the second position at the fourth time.
 11. Theon-car disc brake lathe system of claim 5 wherein: the first and secondadjustment discs comprise slant discs that each include a slantedsurface, and the adjustment discs are arranged so that the slantedsurfaces are opposed to each other in an abutting relationship.
 12. Theon-car disc brake lathe system of claim 6 further comprising a firstgear train operably associated with the first stop disc and a secondgear train operably associated with the second stop disc, the geartrains being configured to follow the movement of the respective stopdisc, the first gear train being operably associated with the firstadjustment disc, and the second gear train being operably associatedwith the second adjustment disc.
 13. The on-car disc brake lathe systemof claim 9 further comprising a first gear train operably associatedwith the first and third stop discs and a second gear train operablyassociated with the second and fourth stop discs, the gear trains beingconfigured to follow the movement of the respective stop discs, thefirst gear train being operably associated with the first adjustmentdisc, and the second gear train being operably associated with thesecond adjustment disc.
 14. The on-car disc brake lathe system of claim13 wherein each gear train is configured such that the associatedadjustment disc is caused to rotate in a first rotational direction whenone of the pair of stop discs associated with the gear train stopsrotating, and the associated adjustment disc is caused to rotate in arotational direction opposite to the first rotational direction when theother of the pair of stop discs associated with the gear train stopsrotating.
 15. The on-car disc brake lathe system of claim 2 wherein thestop disc comprises a starwheel having protruding teeth.
 16. The on-cardisc brake lathe system of claim 15 wherein the adjustment mechanismfurther comprises a stop mechanism associated with the stop disc andoperable to move between a first position in which the stop discoperates in the first state and a second position in which the stop discis caused to operate in the second state.
 17. The on-car disc brakelathe system of claim 16 wherein the stop mechanism includes anelectromagnetic element and a toothed catch member operable to engage atleast one tooth of the starwheel.
 18. The on-car disc brake lathe systemof claim 17 wherein the controller is configured to time actuation ofthe electromagnetic element such that the toothed catch moves into itsfirst stop position to contact a specified tooth of the starwheel. 19.The on-car disc brake lathe system of claim 1 further comprising a drawbar extending through the body of the lathe and the alignment system andoperable for connection to a hub adaptor of a vehicle brake assembly.20. The on-car disc brake lathe system of claim 1 further comprising acomponent for measuring lateral runout of a brake disc and providing themeasurement to the electronic controller, wherein the electroniccontroller issues commands to the adjustment mechanism based on themeasurement.
 21. An automatic alignment assembly for use in an on-cardisc brake lathe system for resurfacing a brake disc of a vehicle brakeassembly, the alignment system comprising: an electronic controller; aninput adaptor configured to rotate with a drive shaft of a brake lathesystem; an output adaptor configured to rotate with the drive shaft; atleast one adjustment disc positioned between the input adaptor and theoutput adaptor, wherein an axial alignment of the input adaptor relativeto the output adaptor may be varied based on a rotational orientation ofthe adjustment disc; and an adjustment mechanism configured to changethe rotational orientation of the adjustment disc in response tocommands from the electronic controller.
 22. The automatic alignmentassembly of claim 21 wherein the adjustment mechanism comprises a stopdisc operable in a first state to follow the rotation of the drive shaftand operable in a second state to rotate relative to the rotation of thedrive shaft to change the rotational orientation of the adjustment disc.23. The automatic alignment assembly of claim 22 wherein the adjustmentmechanism further comprises a stop mechanism associated with the stopdisc and operable to move between a first position in which the stopdisc operates in the first state and a second position in which the stopdisc is caused to operate in the second state.
 24. The automaticalignment assembly of claim 23 wherein: the at least one stop disccomprises a pair of stop discs, the first stop disc operates in thefirst state when the stop mechanism is in the first position, operatesin the second state when the stop mechanism is in the second position ata first time, and operates in the first state when the stop mechanism isin the second position at a second time different from the first time,and the second stop disc operates in the first state when the stopmechanism is in the first position and when the stop mechanism is in thesecond position at the first time, and operates in the second state whenthe stop mechanism is in the second position at the second time.
 25. Theautomatic alignment assembly of claim 21 further comprising a secondadjustment disc positioned between the input adaptor and the outputadaptor, wherein the axial alignment of the input adaptor relative tothe output adaptor may be varied based on the rotational orientation ofthe adjustment discs relative to each other.
 26. The automatic alignmentassembly of claim 25 wherein: the adjustment mechanism comprises a firststop disc associated with the first adjustment disc and a second stopdisc associated with the second adjustment disc; and each stop disc isoperable in a first state to follow the rotation of the drive shaft andoperable in a second state to rotate relative to the rotation of thedrive shaft to change the rotational orientation of the associatedadjustment disc.
 27. The automatic alignment assembly of claim 26wherein the adjustment mechanism further comprises a stop mechanismassociated with the stop discs.
 28. The automatic alignment assembly ofclaim 27 wherein: the first stop disc operates in the first state whenthe stop mechanism is in the first position, operates in the secondstate when the stop mechanism is in the second position at a first time,and operates in the first state when the stop mechanism is in the secondposition at a second time different from the first time, and the secondstop disc operates in the first state when the stop mechanism is in thefirst position and when the stop mechanism is in the second position atthe first time, and operates in the second state when the stop mechanismis in the second position at the second time.
 29. The automaticalignment assembly of claim 28 wherein: the adjustment mechanismcomprises a third stop disc associated with the first adjustment discand a fourth stop disc associated with the second adjustment disc; andeach stop disc is operable in a first state to follow the rotation ofthe drive shaft and operable in a second state to rotate relative to therotation of the drive shaft to change the rotational orientation of theassociated adjustment disc.
 30. The automatic alignment assembly ofclaim 29 wherein: the third stop disc operates in the first state whenthe stop mechanism is in the first position and when the stop mechanismis in the second position at the first and second times, operates in thesecond state when the stop mechanism is in the second position at athird time different from the first and second times, and operates inthe first state when the stop mechanism is in the second position at afourth time different from the first, second, and third times, and thefourth stop disc operates in the first state when the stop mechanism isin the first position and when the stop mechanism is in the secondposition at the first, second and third times, and operates in thesecond state when the stop mechanism is in the second position at thefourth time.
 31. The automatic alignment assembly of claim 27 wherein:the first and second adjustment discs comprise slant discs that eachinclude a slanted surface, and the adjustment discs are arranged so thatthe slanted surfaces are opposed to each other in an abuttingrelationship.
 32. The automatic alignment assembly of claim 26 furthercomprising a first gear train operably associated with the first stopdisc and a second gear train operably associated with the second stopdisc, the gear trains being configured to follow the movement of therespective stop disc, the first gear train being operably associatedwith the first adjustment disc, and the second gear train being operablyassociated with the second adjustment disc.
 33. The automatic alignmentassembly of claim 29 further comprising a first gear train operablyassociated with the first and third stop discs and a second gear trainoperably associated with the second and fourth stop discs, the geartrains being configured to follow the movement of the respective stopdiscs, the first gear train being operably associated with the firstadjustment disc, and the second gear train being operably associatedwith the second adjustment disc.
 34. The automatic alignment assembly ofclaim 33 wherein each gear train is configured such that the associatedadjustment disc is caused to rotate in a first rotational direction whenone of the pair of stop discs associated with the gear train stopsrotating, and the associated adjustment disc is caused to rotate in arotational direction opposite to the first rotational direction when theother of the pair of stop discs associated with the gear train stopsrotating.
 35. The automatic alignment assembly of claim 32 wherein thestop disc comprises a starwheel having protruding teeth.
 36. Theautomatic alignment assembly of claim 35 wherein the adjustmentmechanism further comprises a stop mechanism associated with the stopdisc and operable to move between a first position in which the stopdisc operates in the first state and a second position in which the stopdisc is caused to operate in the second state.
 37. The automaticalignment assembly of claim 36 wherein the stop mechanism includes anelectromagnetic element and a toothed catch member operable to engage atleast one tooth of the starwheel.
 38. The automatic alignment assemblyof claim 37 wherein the controller is configured to time actuation ofthe electromagnetic element such that the toothed catch moves into itsfirst stop position to contact a specified tooth of the starwheel. 39.The automatic alignment assembly of claim 21 further comprising a drawbar extending through the body of the lathe and the alignment system andoperable for connection to a hub adaptor of a vehicle brake assembly.40. The automatic alignment assembly of claim 21 further comprising acomponent for measuring lateral runout of a brake disc and providing themeasurement to the electronic controller, wherein the electroniccontroller issues commands to the adjustment mechanism based on themeasurement.
 41. An apparatus for aligning the axes of two rotatingshafts comprising: an electronic controller; a first input adaptorconfigured to rotate with a first shaft; a second output adaptorconfigured to rotate with the second shaft; at least one adjustment discpositioned between the input adaptor and the output adaptor, wherein anaxial alignment of the input adaptor relative to the output adaptor maybe varied based on a rotational orientation of the adjustment disc; andan adjustment mechanism configured to change the rotational orientationof the adjustment disc in response to commands from the electroniccontroller.
 42. An on-car disc brake lathe system for resurfacing abrake disc of a vehicle brake assembly, the brake lathe including alathe body with a driving motor, a cutting head operably attached to thebody, and a drive shaft, the on-car brake lathe system further definedby an alignment system comprising: an input adaptor configured to rotatewith the drive shaft; an output adaptor configured to rotate with thedrive shaft; a stop disc system including one or more stop discs; andone or more adjustment discs operable to rotate in response to therelative rotation of at least one stop disc, the adjustment discs beingoperable to adjust the axial alignment of the drive shaft with respectto an axis of rotation of a brake disc.
 43. An on-car disc brake lathesystem of claim 42 further comprising a stop mechanism associated withthe stop disc system wherein the stop mechanism is operable to cause atleast one of the stop discs to rotate.
 44. The on-car disc brake lathesystem of claim 43 wherein: the one or more stop discs comprise twopairs of stop discs, and the one or more stop mechanisms comprise asingle stop mechanism operable to cause any of the stop discs to rotate.45. The on-car disc brake lathe system of claim 43 wherein the stopdiscs are rotatably secured to the input adaptor such that the stopdiscs rotate with the input adaptor and such that the stop mechanism isoperable to cause any of the stop discs to rotate relative to the inputadaptor.
 46. The on-car disc brake lathe system of claim 45 wherein thestop discs comprise starwheels having a plurality of protruding teeth.47. The on-car disc brake lathe system of claim 46 wherein the stopmechanism comprises an electromagnetic element and a toothed catchmember operable to engage at least one of the plurality of teeth of thestarwheels.
 48. The on-car disc brake lathe system of claim 47 furthercomprising means for timing the actuation of the stop mechanism suchthat the toothed catch member contacts a specified stop disc uponreceipt of a control signal.
 49. An on-car disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly, the brake lathecomprising a lathe body with a driving motor, a cutting head operablyattached to the body, and a drive shaft, the on-car brake lathe systemfurther defined by an alignment system comprising: an input adaptorconfigured to rotate with the drive shaft; an output adaptor configuredto rotate with the drive shaft; a stop disc system comprising two pairsof stop discs and a stop mechanism operable to cause any of the stopdiscs to rotate; and one or more adjustment discs operable to rotate inresponse to the relative rotation of at least one stop disc, theadjustment discs configured to be capable of adjusting the axialalignment of the drive shaft with respect to an axis of rotation of abrake disc.